Radiation Damage to Cell Molecules

Target Theory

• Cells contain many species of molecules, most of which exist in excess, making them less susceptible to radiation damage.
• However, some molecules are essential for normal cell function and are present in limited quantities, making them vulnerable to radiation damage.
• Radiation damage to these critical molecules can severely affect the cell because there are no substitutes available.
• The target theory is based on the concept of a sensitive key molecule that must be inactivated for a cell to die after radiation exposure.
• DNA is considered the target molecule.

Target Molecule

• The target molecule is an area of the cell occupied by the molecule or a sensitive site on the molecule.
• The target area changes position over time due to intracellular molecular movement.
• The interaction between radiation and cellular components is random, with no preference for the target molecule.

Radiation Interaction

• When radiation interacts with the target molecule, it is considered a "hit."
• Radiation can also interact with molecules other than the target molecule, resulting in indirect effects.
• It is not possible to distinguish between direct and indirect hits.
• Hits occur through both direct and indirect effects of radiation.